Variable focus transducer



May 14, 1963 o. H. SCHUCK VARIABLE 1=*ocus TRANSDUCER 2 Sheets-Sheec 1Filed Sept. 9. 1957 GENERATOR TRANSMITTER 78 May 14, 1963 o. H. SCHUCKVARIABLE FOCUS TRANSDUCER 2 Sheets-Sheet 2 Filed Sept. 9. 1957 A TTORNEY United States Patent O 3,090030 VARIABLE FOCUS TRANSDUCER Oscar HugoSchuck, Minneapolis, Minn., assignor to Minneapolis-Honeywell RegulatorCompany, Minneapolis, Mirm., a corporation 01 Delaware Fileti Sept. 9,1957, Ser. N0. 682,791 3 Claims. (Cl. 340-16) This invention relates totransducers and is more partieularly related to the variable focusing ofa bilateral transducer to be used for transmitting and receiving in apropagative Wave system.

It has been known for sorne time in the prior art that a bilateraltransducer of this general type was capable of producing an outputpattern which could be caused to focus at a particular given distancefrom the surface of the transducer. T'nis has been accomplished byroviding the transducer itself with a spherical or curved surface havinga radius of curvature equal to the dis-tance at Which the focal pointwas desired. This scheme produced a satisfactory transducer which hadthe shortcoming of having only one center of -focus and also wasdifiicult to produce for short foeal lengths.

It is an object of: this invention -to provide a variable focustransducer which may be controlled according to a tirne va.ried functionso as to provide a sweeping eflect between varying distarxces from thetransducer.

Other objects and advantages of rny invention will become apparent tothose skilled in the art, from a reading of the appended speeification,claims and drawing in which:

FIGURE 1 is an illustration, largely schematic, of a variable focustransducer embodied as a receiver for observing the presence andlocation of a source of oscillatory energy;

FIGURE 2 is a front view of the variable focus transducer shown inFIGURE 1;

FIGURE 3 is a sehernatic diagram of another embodiment in which avariable focus transducer is utilized in conjunetion with a -transmitterto propagate oscillatory energy into a mediurn; and

FIGURE 4 is a d-iagram illustrating some of the mathematical principlesto aid in explaining the operation.

FIGURE 5 is a block diagram of an echo-ranging systern of rny inventionincluding a variable focus transducer.

FIGURE 1 shows a variable focus piezoelectric transducer =10, a sonrceof sound energy 30, to be observed by transducer 10, and indicatingmeans 40, shown as a cathode ray tube indicator, to provide anindication of the output of variable focus transducer '10.

Variable focus transducer cornprises a body of piezoelectric material 11, a first electrode 12, covering the entire face of piezoelectric body1-1, and second and third electrodes =13 and 14 (shown as concentrieannular electrodes) applied to the opposite face of piezoelectricmaterial 1:1. Electrode 14 is an annular concentric ring isolated fromcircular electrode 13 which comprises the central Portion o-f the faceof piezoelectric material 11. The well known properties exhibited bypiezoelectric material are such that a voltage is produced across theelectrodes when the material is mechanically excited. lt is also wellknown that transducers 01 this general type exhib-it a bilateralcharacteristic in that they may also produce a mechanical output Whenelectrically excited. It should be obvious to those skilled in the artthat other types of transducers may be used, in practicing my invention,Where -suita=ble sirnilar outputs are obtainable. It is to be noted thatthe annular shape of the electrodes is used here for purposes ofillustration only. The physical configuration 01 the electrodes isimmaterial as long as a signal may be obtained fromportions of thetransducer that are equi- Palzented May 14, 1963 distant from an axisthrough the center of the transducer and normal to its plane. As anexarnple, one could have a composite transducer made up of a nurnber ofindividual transducers and by choosing -groups of transducers positionedat equal distances from the center of the composite transducer, thefocal point of the composite transducer may also be controlled bysu-itably connecting these groups as described above.

The source of sound, 3, may be a reflector for reflecting energy fromanother source of oscillatory energy or may be a self-contained sourceof oscillatory energy.

Cathode ray -tube indicator 40 is connected to a transformer 41 having aprimary winding 42 and a secondary Winding 43. The right band end ofprirnary winding 42 is connected to first electrode 12 through conductor44. The left hand end of transforrner prirnary winding 42 is connectedto third elec-trode 14 through conductor 45. Second electrode 13, isconnected to the left band end of transformer primary Winding 42 throughconductor 46, phase delay network 20 and conductor 15. It should beobvious to those skilled in the art that cathode ray tube 40 may bereplaced by any suitable signal utilization device or apparatus.

Phase delay network 20 is comprised of an inductor 21, connected at itsright band end to conductor 15, a capacitor 22, connected between theright band end of inductor 21 and concluctor 46, a capacitor 23,connected between the left band end of inductor 21 and conductor 46, anda variable resistance 25, shown as a triode, connected through abat-tery 24 frorn the left band end of inductor 21 to conductor 46.Triode 25 includes the usual plate, grid and cathode electrodesindicated respectively by reference characters 27, 28 and 29. A functiongenerator 26 is utilized to control the conductivity, and thereforeresistance, of triode 25 to control the phase delay provided by thephase delay network 20. Function generator 26 is shown connected betweengrid electrode 28 and cathode ele-otrode 29 so as to control theconductivity of triode 25 in accordance With a voltage generated byfunction generator 26. One example of a device that might be used asfunction generator 26 is shown and described at page 189, aragraph47c(1) of Radar Electronic Fundamentals Navships 900,016, published bythe Bureau of Ships, Navy Department, Inne 1944. The device referred tois a thyratron saw tooth generator having a saw tooth sweep output andwould be used to supply a sweeping effect on the focal point oftransducer 10. More simply, function generator 26 might be a calibratedpotentiorneter energized from a suitable source of potential. lt shouldbe apparen-t to those skilled in the art that phase delay network 20 isan example of only one of many types of hase or tirne delay networks.

FIGURE 2 is a front view of transducer 10 in FIG- URE 1. In FIGURE 2second electrode 13 has a m0- ment arm radius a and third electrode 14has a moment arm a. For purposes of illustration, the sizes ofelectrodes 16 and 14, relative to each other, are shown with electrode13 larger than would normally be used.

FIGU=RE 4 is a diagram showing the conditions required for properfocusing of the variable focus transducer. In FIGURE 4 the firstelectrode 12, the surface norrnally in contact with the medium, andpiezoelectric body 11 have been rernoved to show only the second centralelectrode 13 and the third annular electrode 14. In receiving energy-from a point '50, since the sound arrives at the central secondelectrode 13 before arriving at the third annular electrode 14, a phaseor time delay is necessary to provide a focusing effect. This may bea.rrived by the approximation;

sin cz tan a whcre a-tan d ;b=necessary phase delay in radians, =wavelength in medium, a =rnoment arm of electrode 14, and d=distance tosignal source. It has been observed that optimum focusing may beobtained when a phase or tirne delay, substantially equal to this value,is inserted in the electrical path frorn the second central electrode 13to the cathode ray tube indicator 40.

OPERATION OF FIGURE 1 Assuming for the moment that the functiongenerator 26 is a simple calibrated otentiometer for varying theconductivity and thereby resistance of triode 25 by varying thepotential applied across grid and cathode electrodes 28 and 29, it maybe seen that the sound ernanating frorn source of sound energy 30, atany given distance frorn variable focus transducer 10, Will intersectthe transducer at its center portion at sorne earlier tirne than at itsouter portions. In order to obtain maximum energy from the source ofsound energy 30 it is necessary that all of the signal, emanating frornthe source of sound 30 reach the cathode ray tube indicator 40 at thesarne time. lt is to be understood that time, in the sense used here,may also be expressed as a phased relationsh-ip between two or moreoscillatory signals. This is done by delaying the signal impingin'g onthe central portion of transducer 10, that is central electrode 13, -byan amount of time such that it will be applied to oathode ray tubeindicator 40, at the sarne time the signal received from source of sound30 is applied to cathode ray tube indicator 40 from the third annularelectrode 14 on trans ducer 10. The time delay is accornplished by thevariable phase delay or time delay network 20, which is in turncontrolled by the resistance of triode 25. If a otentiometer is used asfunction generator 26 to control the resistance of triode 2.5, and iscalibrated in distance, the sigmal, comprising the signals frornelectrodes 13 and 14, 1eoeived by cathode ray tube indicator 40 may beadjusted for maxirnurn value by varying the voltage applied to thecontrol grid of triode 25 by the potentiometer rneans and then' readingdirectly on a scale the distance of the source of sound 30 from variablefocus transducer 10.

An example of a transducer used in one embodiment of my inventionfollows;

Material quartz.

Diameter .25 ineh.

Thickness .001 inch.

Eleotrode material silver.

Number of annuli 4.

Frequency rnegaeycles per second.

Amount of phase delay at outer annulus a distance of 1" 4 =.0174microsecond.

The above described transducer was utilized in the field cf medicalresearch for accurately detecting and locating the presence ofnon-hornogeneous areas such as may occur in human flesh as a result ofoancerous growth of the body cells.

lt should be apparent to those skilled in the art that the functiongenerator 26 may be of the type that varies from a maxirnum to a minimumor vice versa and that the cathode ray tube indicator 40 may also, incon'junction with the function generator variation, provide a sweep sothat the variable focus transducer will scan an area frorn a minimurn toa maxirnum distance and provide an indication on the face of theindicator 40 of the distance of a source of sound or energy frorn thevariable focus transducer 10. It should likewise be apparent t0 thoseskilled in the art that the number of annular electrodes, such as shownon the left band face of variable focus transducer 10, is not limited tothe number shown on FIGURE 1 and that the resolution which may beobtained from a variable focus transducer of this nature is increasedwith an increase in the number of annular electrodes. lt should beunderstood that suitable tirne or phase delay networks are insertedbetween each of said annular electrodes and the signal utilization meanssuch as cathode ray tube indicator 40.

Referring now to FIGURE 3; a variable focus transducer 60 is shownadapted to transmit energy from a transmitter 70 so that it may befocused on objects or 91 which are situated =at particular distancesfrom transducer 60.

Transducer 60 includes a piezoelectric body 66, an electrode 67,positioned on the right hand face of piezoelectric body 66, a centralelectrode 64 positioned in the center of the left band face cfpiezoelectric body 66, and con'centric annular electrodes 63 and 62positioned also on the left band face of piezoelectric body 66.

Eleetrode 67 is connected to ground through conductor 65. Centralelectrode 64 is connected to transrnitter 70 through a phase delaynetwork 73 and conductor 71; electrode 63 is connected to transmitter 70through a phase delay network 74 and conductor 71; and electrode 62 isconnected to transmitter 70 through a phase delay network 75 and aconductor 71. Transmitter 70 provides an output for the energization oftransducer 60 through a conductor 71 and to ground through a conductor72.

The phase or time delays alfected by the phase delay networks 73, 74 and75 are controlled by the voltage appearing across potentiometer 85.Phase delay networks 73, 74 and 75 may be similar 10 the type describedabove in connection With FIGURE 1, i.e. the amount of phase delay may becontrolled by the application of a suitable potential to a controldevice incorporated in the phase delay network. Funther, since theamount of delay needed between successive electrodes is not a linearfunction, phase delay networks 73, 74 and 75 may also incorporate ameans responsive to the potential supplied from otentiometer winding formodifying the amount of phase delay as the focal point is moved awayfrom the right side of transducer 60. Adjustable taps 86, 87 and 88 areprovided on otentiometer 85 for adjusting the potential applied to thephase delay networks. Wiper 86 is connected to phase delay network 73through conductor 76; wiper 87 is connected 10 phase delay network 74through conductor 77; and wiper 88 is connected to phase delay network75 through a conductor 78. A triode 83 is utilized to energize -thewinding of potentiometer 85 through a circuit including the plateelectrode 95 of triode 83, battery 84, otentiometer winding 85, andconductor 92 connected to ground at 93 and also to the cathode 97 oftriode 83. Triode 83 includes the usual plate, grid, and cathodeelectrodes indicated respect1vely by reference characters 95, 96 and 97.The conduotion 0f triode 83 is controlled by a function generator shownconnected across the grid and cathode electrodes 96 and 97 of triode 83so as to control the conductivity of triode 83 in accordance with theoutput of function generator 90.

OPERATION OF FIGURE 3 The operation of FIGURE 3 is very similar to thatof FJGURE 1 in that the signal, in this case a transmitted signal, iscaused to be propagated from the various annular sections of transducer60 so that it arrives in phase or at the same tirne at a given point inspace from the face of transducer 60. It is the purpose of the phasedelay networks 73, 74 and 75 to provide the proper delays in theapplication of the signal to transducer 60 so that this phenomenumoccurs.

From a consideration of the two embodiments shown and described above,it should be apparent that the transmitting and receiv=ingcharacteristics may be combined in one device.

Referring now to FIGURE 5 in which a variable focus transducer 100, isconnected to be utilized in conjunction with an echoranging System of atype generally wellknown in the art; the echo-ranging system includes atransmitter 130, a keyer 140, a receiver 150, a sweep generator 146, arelay 110, an indicator 160, and a transducer 100.

Keyer 140 includes a common terminal 143 connected to ground, an outputterminal 141 for providing a signal for activating transmitter 130, anoutput terminal 144 for energizing the winding oftransrnitting-receiving relay 110, and an output terminal 145 forsupplying a signal to initiate the action of sweep generator 146.Transmitter 130 includes a pair of terminals 131 and 132 for connectionto a source of alternating current to supply operating voltage thereto,a common =terrninal 134 comnected to ground, an input terminal 133, andan output terminal 135. Sweep generator 146 includes a cornrnon terminal149 connected to ground, an input terminal 147, and an output terminal148. Receiver 150 includes a pair of terminals 151 and 152 forconnection to a source of alternating current to supply operatin gvoltage thereto, a common terminal 154 connected to ground, an inputte1rninal 153, and an output terminal 155. Indicator 160, which may beof a type comrnonly known in the art as a cathode ray tube indicator,includes a comrnon terminal 165 connected to ground, an input signalterminal 162, and a further swep Signal input terminal 164. The windingof transmitting-receiving relay 110 iS connected gronnd and is adaptedto actuate normally open rnovable relay contacts 111 and 112 andnormally closed movable relay contacts 113 and 114. Stationary relaycontacts 115 and 116 are associated with movable relay contacts 111 and112 respectively. Stationary relay contacts 117 and 118 are associatedwith movable relay contacts 113 and 114 respectively. Phase delaynetwork 126 includes a comxnon terminal 159 connected to ground, controlsignal input terminal 161, Signal input terminal 157, and signal outputterminal 158. Transducer 100 includes a first electrode 101 connected toground at terminal 102, a first annnlar electrode 104, and a secondannular electrode 103. An illustration of the characteristic radia-tionpattern of the transducer When used for transmitting is indicated bydotted line 107.

Output terminal 141 on keyer 140 is connected to input terminal 133 ontransmitter 130 through conductor 142. Output terminal 144 on keyer 140is connected 10 the winding of relay 110 throngh conductor 123. Outputterminal 145 on keyer 140 is connected to input termnal 147 on sweepgenerator 146 through conductor 127. Output terminal 135 on transmitter130 is comnected to rnovable relay contacts 111 and 112 throughconductor 156. Output terminal 148 on sweep generator 146 is connected10 control signal input terminal 161 on phase delay network 126 throughconductors 127 and 128. Outpnt terminal 148 on sweep generator 146 isconnected to control Signal input terminal 164 on indicator 160 throughconductor 127. Input terminal 153 on receiver 150 ds connected tomovable relay contact 114 through conductor 124 and output terminal 155on receiver 150 is connected to signal input terminal 162 on indicator160. Input terminal 157 on phase delay network 126 is connected tomovable relay oontact 113 1hrough conductor 122. Output terminal 158 onphase delay netzwork 126 is connected to input terminal 153 on receiver150 through conductor 125 and conductor 124. Second annular electrode103 on transdueer 100 is connected 10 stationary relay contacts 115 and118 through conductors .120 and 121. First annular electrode 104 ontransducer 100 is connected to stationary relay contacts 116 and 117.

OPERATION OF FIGURE 5 The apparatus shown in FIGURE 5 is a standard typeof echo-ranging System that is well-known in the art with exceptions asWill be noted below. Basically, the operation consists 0f periodicallyilluminating the field of observation, here the field indicated by thedotted line 107, and then scanning the field at progressively increasingdistances with variable focus transducer to determine the presence anddistance of objects existing within the field cf observation. Inoperation, the keyer 140 provides a Signal to activate transmitter 130,to energize the winding of relay so as to connect transrnitter totransducer 100, and to initiate the operation of sweep generator 146.After a Short interval of time, the Signal from the keyer stops and theWinding of relay 110 is deenergized to connect receiver to transducer100 so that any signals received may be applied to indicator 160, andtransrnitter 130 is inoperative.

It may be Seen that the operation of FIGURE 5 may oe divided into twoparts, that is a first transmitting interval in which annular electrodes103 and 104 connect to transmitter 130 through the normally open relaycomtacts 111 and 112; and a second position in which the receiver isconnected to the transducer annular electrodes 103 and 104 through thenormally closed movable comtacts 113 and 114. lt is during this secondoperation of the echo-ranging system that rny invention is utflized toimprove angnlar resolution in longitudinally scanning the area in frontof the transducer by changing the eflective focal point of thetransducer so that it moves an ever increasing distance frorn the faceof the transducer, in FIGURE 5 from left to right. The focusing efiectis provided as explained in the operation of FIGURE 1 in that a phasedelay networl; 126 is used to operate on the signal appearing on secondannular electrode 104 so that Signals reflected from an object, such asobject 106, and received by annular electrodes 103 and 104 Will arriveat the input terminal 153 of receiver 150 in the same hase relationship.

It should be apparent to those skilled in the art that the hase delaynetwork 126 may include a further function generator aS shown in FIGURES1 and 3 to provide the desired relationship between the phase delayapplied to the Signal from annular electrode 104 and the sweep Signalsupplied to indicator from sweep generator 146. It should further beapparent to one skilled in the art that the dimensions of the transducerused in any particular application are commensurate With the desiredoperating characteristics according to the principles of my invention asexplained above in conjunction with FIGURES 1 and 4.

As another example, one might utilize the focusing properties obtainablethrough the use of my invention for both transrnitting and receivingenergy to a field of observation to obtain even greater angularresolution, particularly at relatively short distances.

It should be apparent to those skilled in the art that a hase delay isdesirable where a continuous wave or modulated pulse System is used andthat a time delay is desirable where a pulse system is used fortransmission. It has been observed that if the proper relationshipbetween the phase or tirne delay fo1' each annular elec- (rode ismaintained, the focal point of the propagative Signal may be varied atwill in accordance With the generated signal of the function generator.Various means for providing a suitable relationship between signals oneach annnlar electrode to provide the desired focusing effect will beapparent to those skilled in the art.

lt should now be apparent to those skilled in the art that transducers10, 60, and 100 may be of the bilateral type, i.e. transducers that maybe used as transmitters 01' receivers of oscillatory energy and that anadjustable focus action may be obtained either in transm-itting orreceiving.

1't has been observecl that the accuracy of focusing and azimuthalresolution will be increased With an increase in the total nurnber ofelectrodes used.

These und otner embodiments and modifications will be apparent to thoseskilled in tne art and it is therefore my Wish to be limited only by thescope of the appended clairns.

I claim:

1. Control apparatus for a wave transducer to produce a sweep focusthereof as a function of time, cornprising;

bilateral voltage transducer rneans having first and second concentricelectrodes formed in a given plane ancl defining an axis normal to saidplane,

voltage responsive means,

circuit means connecting one of said electrodes to said voltageresponsive rneans,

variable phase control means,

circuit means, including said phase control means,

connecting tne other of said electrodes to said voltage responsiverneans,

and sweep control means connected in contrlling relation to said phasecontrol rneans to continuously vary, as a function of tirne, therelative phase between the voltages received by said voltage responsivemeans from said first and second concentric electrodes t0 provide acontinuously variable focus of said transducer means along said axis.

2. In combination, transducer means having a disc formed of a materialhaving piezoelectric properties, a first planar electrode formed on onesurface of said disc, 811d a plurality of concentric planar electrodesformed on a surface of said disc spaced from said one surface of saiddisc, said transducer means having an axis generally normal to theplanes 0f said first electrode and said plurality of electrodes,

signal responsive rneans,

circuit means connecting one of said electrodes to said signalresponsive means,

variable signal delay rneans,

circuit means, including said variable signal delay means, connectingthe other of said concentric electrodes to said signal responsive means,

sweep generator means,

and circuit means connecting said sweep generator means in controllingrelation to said signal delay means to vary the degreeof Signal delay asa function of time 10 provide variable focusing of said transducer meansalo'ng said axis, as csntrolled by said sweep generatorrneans.

3. Energy translating apparatus including bilateral energy transducermeans having first and second concentrie electrodes positioned in agiven plane on one surfaee of said energy transducer means, and having afurther electrode positioned in a second plane on a sunface of saidenergy transducer means which is spaced from said one surface,

voltage responsive rneans,

means connecting one cf said electrodes to said voltage responsivemeans,

voltage controlling means for controlling the relative time relationshipbetween a voltage applied at the input thereof and a resulting voltageappearing at the output thereof,

means including said voltage controlling means comnecting the other ofsaid electrodes to said voltage responsive means, the input 0f saidvoltage controlling means being connected to said other electrode andthe output of said voltage controlling means being connected to saidvoltage responsive means, and further rneans connected in controllingrelation to said voltage controlling means to control said voltagecontrolling means as a function of time so tl1at the relative tirnerelationship between the Voltages received by said voltage responsivemeans from said first and second concentric electrodes is caused to varyas a function cf tirne to provicle variable focusing cf said transducermeans along said axis.

Referenees Cited in the file of this patent UNITED STATES PATENTS

1. CONTROL APPARATUS FOR A WAVE TRANSDUCER TO PRODUCE A SWEEP FOCUSTHEREOF AS A FUNCTION OF TIME, COMPRISING; BILATERAL VOLTAGE TRANSDUCERMEANS HAVING FIRST AND SECOND CONCENTRIC ELECTRODES FORMED IN A GIVENPLANE AND DEFINING AN AXIS NORMAL TO SAID PLANE, VOLTAGE RESPONSIVEMEANS, CIRCUIT MEANS CONNECTING ONE OF SAID ELECTRODES TO SAID VOLTAGERESPONSIVE MEANS, VARIABLE PHASE CONTROL MEANS, CIRCUIT MEANS, INCLUDINGSAID PHASE CONTROL MEANS, CONNECTING THE OTHER OF SAID ELECTRODES TOSAID VOLTAGE RESPONSIVE MEANS, AND SWEEP CONTROL MEANS CONNECTED INCONTROLLING RELATION TO SAID PHASE CONTROL MEANS TO CONTINUOUSLY VARY,AS A FUNCTION OF TIME, THE RELATIVE PHASE BE-